1. Field of the Invention
The present invention relates to a high voltage discharge lamp device, and more specifically to a simplification of the construction thereof.
2. Description of the Prior Art
Conventionally, various high voltage discharge lamp devices have been disclosed. Some of those devices are formed with structures as respectively shown in FIGS. 13 and 14, wherein FIG. 13 is a block diagram of a first embodiment according to the conventional art. In the figure, when a power switch 2 is closed, that is when the power switch is set to on, a voltage generated by a battery 1 is fed to a step-up DC-DC converter 3, and the stepped-up direct voltage generated therein is further fed to an inverter circuit 4 so as to supply an alternating voltage to an igniter circuit 5-1 therefrom. The high voltage generated at the igniter circuit 5-1 is applied to a high voltage discharge lamp 6 and induces a discharge in the gas enclosed in the discharge lamp, whereby the high voltage discharge lamp 6 is lit by the alternating voltage supplied from the inverter circuit 4. A control circuit 7-1, after the high voltage discharge lamp device 6 is lit, adjusts the output voltage of the step-up DC-DC converter 3 and thus controls the electric power to be fed to the high voltage discharge lamp 6 so the high voltage discharge lamp provides a constant illumination.
FIG. 14 shows a block diagram of a second embodiment according to conventional art. In the figure, when the power switch 2 is closed, a voltage generated by a battery 1 is fed to a step-up DC-DC converter 3, and the stepped-up direct voltage produced therein is further fed to an inverter circuit 4 so as to supply an alternating voltage to an igniter circuit 5-2 therefrom. The high voltage generated at the igniter circuit 5-2 is applied to a high voltage discharge lamp 6 and induces a discharge in the gas enclosed in the discharge lamp, whereby the alternating voltage supplied from the inverter circuit 4 by way of coils 10a and 10b lights the high voltage discharge lamp 6. These coils 10a and 10b prevent the discharge inception voltage generated in the igniter circuit 5-2 from flowing back to the inverter circuit 4. A control circuit 7-2, after the high voltage discharge lamp device 6 is lit, adjusts the output voltage of the step-up DC-DC converter 3 and thus controls the electric power fed to the high voltage discharge lamp 6 so the high voltage discharge lamp provides a constant illumination.
FIG. 15 shows a detailed circuit construction of the step-up DC-DC converter 3 and the inverter circuit 4 disclosed in FIG. 14, wherein a condenser 31 and the primary winding of a transformer 32 together form a resonance circuit, and a transistor 33 is alternatively switched at a high frequency by the control circuit 7-2, so that the stepped-up high-frequency voltage is outputted from the secondary winding of the transformer 32. A diode 34 and a condenser 35 from a smoothing circuit which converts the high-frequency voltage fed from the transformer 32 to a DC voltage. Transistors 41, 42, 43 and 44 are connected in a bridge circuit to form an inverter circuit 4, and the respective base terminals thereof are connected to an oscillating circuit 46 by a driver circuit 45. The oscillating circuit 46 generates a low-frequency signal (400 Hz). The resistors 61 and 62 are connected to limit the current flowing into the high voltage discharge lamp device 6.
FIG. 16 shows a timing chart showing an operation of each of the circuits shown in FIG. 15, wherein FIG. 16(A) represents a waveform of the transistor 33, and an output voltage of the step-up DC-DC converter 3 is determined by an ON/OFF ratio of this transistor 33. FIG. 16(B) represents an electric voltage charged in the condenser 35, that is an output voltage of the step-up DC-DC converter 3. FIG. 16(C) represents on/off states of the transistors 41 and 44 which are activated in synchronization with the output of the oscillating circuit 46. FIG. 16(D) represents equally on/off states of the transistors 43 and 42, so that when the transistor 41 of the power supply side is on, then the transistor 44 of the ground side is set to on, and conversely, when the transistor 43 of the power supply side is on, then the transistor 42 of the ground side is set to on. FIG. 16(E) represents a voltage applied to the high voltage discharge lamp 6, and it is noted thereby that an alternating voltage of a low-frequency wave is applied to the high voltage discharge lamp in this manner.
Generally it is impossible to activate a high voltage discharge lamp by a direct voltage due to the fact that it likely causes damage to the electrode of the discharge lamp, and for this reason, the direct voltage is converted to an alternating voltage by an inverter circuit and then supplied to the discharge lamp as shown in the first and second embodiment of the conventional art. However, the fact remains that the manufacturing cost thereof may be high since the inverter circuit requires a power switching element of a high output level, and a specific circuit is required to activate this switching element.